As is well known, vena caval catheters are used during surgical procedures on the heart or an adjacent blood vessels to connect the vena cavae into a cardio-pulmonary by-pass extracorporeal circulation system. Generally, the extracorporeal system includes a blood oxygenator, defoamer, heat exchanger to control body temperature, an air bubble trap, a particulate filter, and a blood pump for returning oxygenated blood to the arterial system of the patient.
In one standard method of employing vena caval catheters to effect venous return catheterization, two vena caval catheters are inserted independently into the atrium. One of the catheters is directed into the inferior vena cava and the other catheter is directed into the superior vena cava. Tourniquets are sometimes used to close the vena cavae about the catheters, so that substantially bloodless surgery may be performed on the heart or adjacent vessels. Venus blood from the upper extremeties of the body flows in the superior vena cava and into the tip of the vena caval or return catheter that is directed into that vena cava. Blood from the trunk and lower extremities of the patient flows in the inferior vena cava and into the tip of the return catheter disposed in that vena cava. In certain cases, a complete by-pass is not employed, for example, a single vena caval catheter may be used where the heart is not to be opened. For example, a two-stage vena caval or venous return catheter having an open end and sidewall openings may be inserted through the right atrium and into the inferior vena cava for draining venous blood into the extracorporeal circulation system. Venous blood, in such case, can flow from the inferior vena cava into the end opening of the dual-stage catheter and blood from the right atrium can flow into the openings in the sidewall of the catheter. Because the walls of the vena cava are flexible, some vena caval catheters have been provided with molded, cage-like tips so that the walls of the vena cava cannot close the inlet or tip of the catheter.
Known vena caval catheters have not been entirely satisfactory for one reason or another. The shape of the catheter tip through which blood enters the catheter has, in some cases, resulted in poor hemodynamic porperties. For example, surfaces at the tip may effect relatively high flow resistances, thus causing undesireable pressure drops as the blood flows into the catheter tip and this tends to increase blood hemolysis. In some cases, surfaces may not be washed with blood thereby increasing the danger of creating initial stages of thrombosis, especially if anitcoagulant levels become low.